Shock absorber



3 Sheets-Sheet 1 M Y o n TA 0 N NM r R w m m NR T IE A 2 uM&

c. R. MAYO ET AL snocx ABSORBER A118. 19, 1952 c. R. MAYO El AL 2 ,4

SHOCK ABSORBER Filed 'Jan. 22, 1949 s Sheets-Sheet 2 as I '56 30 0 0/0 5 57 1 g 7W 37 1 f5 4/ I 55 35 i 2y i 36 :Li 39 5 l Aug. 19, 1952 c. R. MAYO El AL SHOCK ABSORBER Filed Jan. 22, 1949 3 Sheets-Sheet 5 INVENTORS ('zroe R. Nave w .lYn/PM; Marc/15R of the piston rod as Patented Aug. 19, 1952 SHOCK ABSORBER Clyde R. Mayo, Fairfield, Ill., and Morris Katcher, New York, N. Y.; said Mayo assignor to said Katcher Application January 22, 1949, Serial No. 72,126

19 Claims.

This invention relates to hydraulic shock absorbers, particularly to the direct action fluid displacement type in which a cylinder structure and a piston structure are relatively reciprocable longitudinally or axially for displacement of fluid against flow resistance. In the use of such shock absorbers, as for example for damping purposes in automobiles, in airplane landing gears, or on guns for damping the recoil, eflicient operation of the shock absorber requires that the space in which the piston operates be at all times kept filled with hydraulic fluid to the exclusion of air. Compensating means must be provided to compensate for increase or decrease of the volume of the fluid due-to temperature changes and also to compensate for displacement of hydraulic fluid-by the volume it enters or leaves the cylinder.

In the design of prior shock absorbers, complicated valving is required for expelling and admitting fluid to and from a reservoir as the piston rod moves in and out of the main cylinder. Such valving in some designs limits the operational characteristics. The uncontrolled flow of fluid to and from the reservoir tends to produce foam. If foam or air gets into the main or working cylinder, the operation of the unit is impaired, because foam'or air in the cylinder acts as a cushion to prevent the building up of the desired damping pressures.

It is an object of the present invention to provide means for keeping the fluid in the main cylinder of the shock absorber under a relatively high pressure to prevent the entrance of air. This is accomplished by providing a compensating piston operating in an auxiliary or compensating cylinder, which compensating cylinder is in fluid communicating with the main cylinder.

In one form of our shock absorber, the compensating piston and the compensating cylinder are in axial alignment with, the main piston and main cylinder respectively. In another form the compensating piston and compensating cylinder are to one side of the maincylinder. In both forms the compensating cylinder is under relativelylheavy spring pressure for forcing back into the main cylinder fluid present in the compensating cylinder. A further object of our invention is the prevention of the foaming usually. caused in a shock absorber where the liquid is discharged or received from the main cylinder in accordance with the'reciprocation of the piston rod into and out of the main cylinder.

Inour construction, liquid is forced out of'the 2 v main cylinder as the piston rod enters it, the liquid forced out pushing back the compensating piston against the spring acting against the latter. Upon the withdrawal or outward motion of the. piston I rod, the compensating piston force's back the fluid which was previously forcedfout of the main cylinder. The spring pressure is strong enough, except for extremely violent jolts, to force fluid through valves provided in the main piston against the resistance'of the flow of fluid through said valves.

When a joltoccurs which is violent enough to increase'the' resistance to flow of the fluid through the piston valves sufliciently to overcome the pressure of the compensating piston,

the latter is' forced back against the pressure of its spring providing thereby a maximum limit tothe force that can be developed.

In our design the relative diameter of the main cylinder is large to that of the cross sectional area of the rod. As will become evident hereinafter, this is done to reduce the effect of pushing out the piston rod that is produced.

by the pressure of the compensating piston on the fluid in the main piston. The volume of fluid required to pass through the piston valves will be greater with a larger diameter cylinder. Increased volume of flow requires the larger fluid passages that are provided in our shock absorber. Larger passages are easier to manufacture and are less critical in tolerances.

A further object of our construction is'a piston valve of simple design that opens in steps-or to greater extent successively with resilient resistance as the pressure increases when the piston moves in the main cylinder. In the particular embodiment illustrated this takes place with movement of the piston outward'of the" main cylinder. The reverse could have been-selected.

Such a design permits wide variations in openings for the different pressures, and makes possible a 'widerange in both the magnitude and kind of the operating characteristics. The resistance of the flow of fluid through the valve means for outward movement of the piston relative to the resistance through the valve means I greater or less. sistance .is provided in the construction of' the for'inward movement of the piston may be made Said relative difference in rev .The form of .shock absorber in which/the compensating piston is in axial alignment" with the mainpiston, under certain conditions, requires more room between the points of attachment at theends of the shock absorber than is position.

the main cylinder, when the rod moves in, for

only a limited motion of the compensating piston. After that, further overflow because of further inward motion of the rod escapes through a port directly into the reservoir. Where the compensating piston is to one side of the main cylinder, the motion of the compensating piston can readily be sufficient to provide for the full amount of overflow. However, even with the latter construction, an overflow port is provided but for another reason as will be explained.

Other objects and advantages will become apparent upon further study of the description and drawings in which:

in Fig. 9, spacer 22 is provided with upstanding lugs 23 and 93 which come between cylinders l8 and i9 and keep the cylinders concentric. The downstanding lugs 93 keep the bottom of cylinder IS a distance above cap 2|. The center of spacer 22 is provided with a depression 25 having a hole 26. A valve discZl' is nested in depression 25 and pressed down therein by plate spring 28 gripped between the bottom of cylinder l8 and spacer 22.

Compensating cylinder 29 is set on top of spacer 26. A cup-shaped closure 39 is set on top of cylinder 29. On top of closure 30 is set a retainer 3|, the upper edge of reservoir cylinder I9 being Fig. l is an elevation of the shock absorber in not quite fully telescoped condition, the compensating piston being in axial alignment ith the main piston. v

Fig. 2"is a vertical section with the shock absorber partially telescoped, the compensating piston being nevertheless against its stop, as is the" case, because of'leakage, when the shock absorberis idle for a sufficient length of time.

Fig.3 is a section taken along 3-3 of Fig. 2 which is just below the compensating piston.

Fig. 4 is a sectiontaken along the line 44 of Fig. 2.

Fig.5 is a section taken along the line 55 of Fig- 2. I V Fig. 6 is a vertical section to a larger scale with the. shock absorber largely telescoped. 7 is a partial vertical section showing a modified mounting for the cylinders and piston rod, the piston rod being largely withdrawn and .the main piston in outward position in the main cylinder.

Fig. 8 is a section taken along the of Fig. 7.

Fig. 9 is a perspective of the closure of the botline 8-8 tom of the main cylinder.

Fig. 10 is' a partial section to an enlarged scale of the valve plate and main piston, the valve spring being omitted.

Fig. 11 is a vertical section of a modified form of the shock absorber in which the compensating piston is to one side of the main piston. The shock absorber is shown in partially telescoped Fig. 12 is a vertical section of the shock absorber of Fig. 11 shown substantially fully extended. 4

Fig.'l3 is a vertical section showing the shock absorber of Fig. 11 substantially fully telescoped, and I Fig. 14 is a section taken along the line l4l4 of Fig. 11.

Referring to Figs. 1-10, the piston rod I5 is adapted at its upper end to be attached to the frame of the vehicle. Fixed to piston rod I5 near its upper end is a cylindrical shield l6. Fixed to the lower end of rod, i5 is the piston denoted in its entirety by the? numeral l1} Piston l1 opcrates in main cylinder l8. Surrounding and concentric with main cylinder I8 islreservoir cylinder l9. relation by spacer 20. The lower end of cylinder i9 is closed by a cap 2| which is fixed to it and is adapted to be fastened, to a wheel support. Inside of cap 2] is a spacer 22 which isat the bottom of main. cylinder I8 and acts to hold it concentric with reservoir cylinder l9. As' seen Cylinders l8 and I9 are kept in spaced,

crimped over retainer 3|, thereby holding all parts tightly together. The edges of retainer 3| are turned down over the outside of cylinder 29 to act as a spacer between cylinders l9 and 29. A spring 32 in closure forces plate 33 against packing material 34 to prevent leakage along piston rod l5.

Compensating piston 35 isslidably mounted in compensating cylinder 29. It is also slidably mounted on piston rod [5 through the intermediacy of channel-shaped synthetic rubber packing ring 36. The hole in the bottom of piston 35, through which piston rod [5 passes, is larger than the external diameter of the web of ring 36. The web of ring 36 has a sliding fit on piston rod i5; When fluid pressureforces the lower'flange of ring 36 up against the bottom wall of piston 35, leakage'of fluid into space 3'! above said piston will be almost completely prevented. Binding of compensating piston 35'onrod l5, should any eccentricity be present, will be prevented because the opening in the bottom of the piston is larger than the outside diameter of the web of ring 36.

Fluid is free to flow through'ports 39 in spacer 29 when forced up from the space or chamber 38 below spacer 20 and above main piston ll. Free communication for fluid is also provided by ports 40 between lower reservoir chamber 42 and upper reservoir chamber 4|. Ports 55 are provided in compensating cylinder 29 at a predetermined distance above spacer 2U and'at a still higher elevation are other ports 56'. These ports provide communication between chamber 4| and 'compensating cylinder 29. A relatively powerful spring 51 normally holds piston 35 down against stop or spacer 29.

The piston assembly I! consists of'a piston cup 43 held against a shoulder on rod l5 by the nut 44'. V The piston contains valves for controlling theflow of fluid in either direction. Rod l5 has an axial passage 45 which opens at its lower end "chamber 54 to chamber 38 but not in the reverse direction. There are three openings 50, Figs. 4 and 10, in piston cup 43'for connecting'chamb'ers 38 and 54. These openings are unequally spaced circumferentially around "the longitudinal axis of rod. l5 so that the force acting through said openings to push down thecovering valve plate 5I'fr'om the openings will, act unequallyagainst spring 52 which acts equally all around the plate to push said plate up against said openings.

Each'iopening is. provided with a downwardly projecting boss 53 .which'has a good surface for sealing when plate 51 is in contact with it; Said bosses also provide pivot points when plate 5| is pushed from first one then another of the bosses. Openings 5B are enlarged at their lower end to provide a larger working force against plate 5| than wouldoccur'from their smaller upper end. The enlargement of the openingsi also helps to provide a reduced resistance to flow-byv plate 5| as said plate opens. In addition to controlled openings 50 in pistoncup 43, there is a free openingorport 65.

Figs. 7 and 8 show a spacer 58 of a form modifled from that of spacer of Figs. 2 and 6. It consists of a ringhaving an upturned .flange 59 with notches 60 .in its periphery. Flange 59 serves to hold compensating cylinder 29 in spaced relation reservoir cylinder. l9, notches 60 afiording communication for fluid between upper-reservoir chamber 4| and lower reservoir' chamber 42. Downwardly projecting flange 6| maintains main cylinder'lB in its relative position to the other adjacent cylinders.

In normal. operation, chambers 38 and 54 are filled with hydraulic fluid. When the. main piston I1 is near the upper end of its stroke, as is the case, Fig. '7,upon a large recoil of the vehicle springs, not shown, chamber 4| is empty and chamber 42 is partly full with compensating piston resting on spacer 20. When the vehicle springs are compressed, as when the vehicle strikes a :bump in the road, main piston moves inward to near the bottom of cylinder |:8 as shown in'Fig. 6. Because of the added length of piston rod l5 now in chamber 38, more hydraulic liquid is displaced by it than when piston I1 is near the top of said chamber as in Fig. '7. Therefore when piston H is down, as in Fig. 6, chambers 38 and 54 are filled with liquid, reservoir chamber 4| is largely filled and-compensating piston 35 is lifted, against the pressure of spring 51, off spacer 20 by liquid entering space 62 between them. As piston I1 is moved down into cylinder l8, compensating 'piston35 is lifted up from spacer 20 by the flow of liquid through ports 39. Compensating piston 35 rises only until it uncovers port 55 in compensating cylinder 29. Once this happens, th additional fluid, forced into space 62 by the entrance of more of piston rod l5 into chamber 38, passes through ports 55 into reservoir chamber 4|. Ports 55 are provided to keep down the length of compensating cylinder 29 by limiting the travel of compensating piston 35. This is necessary when the distance available between the placesof attachment 63 and 64 of the shock absorber requires it.

The spring 51, pushing down on compensating piston 35, produces a pressure in the hydraulic fluid in chambers 38 and 54. If piston-rod I5 is not moving there is no pressure drop across the piston I1 and the pressures in chambers 38 and 54 are equalized through port 65. When the piston rod I5 is moved fluid must flow through the piston valves and port 65 causing a pressure differential between chambers 38 and 54. The pressure in' chamber 38 is determined by the spring force on the compensating piston 35 and is therefor nearly constant. The pressure in chamber 54 rises when the piston rod |5 moves downward and falls when said rod moves up. To

compensate for the .volume of piston rod l5 as it reciprocates, the combined volumes of chambers 38 and 54 must increase and decrease as the rod moves down or up or provision must be made to let fluid move to and from reservoir chambers 4| and 42. Instead, the action of the compensati piston 35 is used to change the total volume 6 of chambers 38 and 54 to compensate for the volume of piston rod l5. When piston rod |5 moves down, compensating piston 35 moves upto allow for the volume of rod |5 that comes into chamber 38. When piston rod I5 moves up, com.- pensating piston 35 moves down to fill in the volume vacated by rod |5.- When piston rod |5 moves down farther than a predetermined amount, compensatin piston 35 is moved up to .clear ports 55 which allow the aditional volume of displaced fluid to pass into chamber 4|. :When piston rod l5 moves up more than a predetermined amount oo-mpensating piston 35 is moved down until it rests on spacer 20. Once piston 35 reaches spacer 28,. the pressur said piston exerts, because of spring 57, on the .fiuid in chambers 38 and 54 will disappear. This makes it. possible for fluid to enter chamber 54 around check valve plate 21. to fill in any volume vacated by further upward movement of the rod.

' V The action of piston valves 48 and. 5| is as follows: During the upward movement of piston I1, the pressure in chamber38 is greater than in chamber 54. At low speed upward, the fluid will pass through free opening 65. At higher speeds upward, the pressure diiference between chambers 38 and 54 will be built up to the point where openings .50 will be uncovered, some. openings 50 more than others, permitting an increase of fluid flolw and thereby preventing the pressure in chamber 38 from rising: too rapidly. At still higherspeeds upward, the other openings .50 will :be successively more uncovered as the pressure becomes high enough to overcome the spring induced pressure of plate 5| against bossesp53. It is thus seen that fluid is permitted to pass the piston in proportion to the speed and travel of the blow received by the shock absorber. Our shock absorber produces a greater damping effeet by permitting more fluid to pass the piston by increasing the area of opening through it as the intensity of the blow is increased than would be the case if there were a fixed area of opening. As the velocity of the main piston is increased, the rate of flow of liquid through said piston increases. Thisv would normally increase the pressure in chamber 38, but by the action of plate 5| to free openings 50 to a greater extent as the rate of flow is increased, this increase in pressure can be regulated as desired.

. By changing the size of opening 65, or of any of openings 50 or the amount of force on each boss 53. by the relative spacing of openings 50,. or by changing the strength of spring 52, or by changing the area of the openings through said bosses, Fig. 10, it is possible to obtain a large range of damping effect. By proper balancing of these items, a uniform resistance to the flow of fluid through the (piston may be obtained for difierent velocities of said piston.

If the upward speed of piston I1 is faster than i a predetermined amount, the relief of pressure effected by the flow of fluid through piston may be insufficient to prevent a suflicient pressure from developing in chamber 38 to push compensating piston 35 upward against its spring 51. The normal motion of piston 35 is downward when piston ll rises. When, however, piston 35 is forced upward, as just noted, fluid will be sucked past check valve 21 to supply fluid for filling up the space produced between piston 35 and spacer 20. If piston 35 should be pushed above ports 55, fluid will pass into chambers 4| .and 42.

On the downward movement of piston rod I5,

aeovyrre free opening 65. At higher speeds the pressure diii eren'cewill become greater until opening 4''! is freed by" the pushin back of ball valve 4'8 against the pressure of its spring 49.

The sealing means 36 between compensating piston 35- and. rod l5 is not entirely proof against leakage. Because of this compensating piston will move down to. spacer 20, as shown in Fig.-v 2, due to slow leakage past sealing means 35- when the shock absorber. is idle for a sumciently' long period. The first stroke of piston H in either direction will make the shock absorberefiective again. If after such a period, piston rod l5 moves down, compensating piston 35' will move up as usual; If, however, rod [5 moves. up first, compensating piston 35 will be unable to move down because it already is in contact with spacer 20. The needed fluid then will enter chambers 38 and 54 via checkvalve 2'! at the bottomv of chamber 54; Compensating piston 35 will liftoff spacer 20 and become effective on the next down stroke of piston I! because of the added fluid.

Should too much fluid leak past sealing means 36into the space 37' above compensating piston 35, said fluid' canv escape into reservoir chamber 41 through ports 56.

In Figs. 11*14, thev compensating piston H is to one side of main piston l1 instead of being in: axial alignment with it as'in Figs.- 1-7. In the construction of the latter figures because of the limited space between places of attachment 63 and 64, when the" compensating piston rose to a height which was not sufiicient to compensate for the added volume of the piston rod resulting from along downward stroke, ports were uncovered. This allowed the excess fluid to pass intoreservoir chamber M. In the construction shown in Figs. 11-14, because the compensating piston TI and compensating chambersBT and 68, and reservoir chamber 69 are to one side of the main piston IT and cylinder 10, the volume of fluid displacing compensating piston 'll can be large enough to compensate for the volume of the piston rod' for the entiredownward stroke of said-rod.

Piston H, which is constructed the same as the one shown in Fig. 6, operates in main cylin der l0. Adjacent to cylinder 10 is compensating. cylinder 66'. Casing 12 surrounds cylinders 10 and H in spaced relation, giving rise to reservoir chamber 69. Cylinders 66 and H, andcasing 69' are mounted in liquid tight relation upon bottom casting T3 and are capped atthe. top by casting 14. Casing. 12' extends up past casting 14 and is capped by casting l6, the'latter serving as a guide for piston rod I5. A suitable packing gland I1 is provided aboutrod I 5 to prevent leakage' of fluid from the shock absorber. To permit the return to reservoir chamber Bil of whatever fluid that'is dragged into space 78 above casting M. a passage 19" isprovided through saidcasting. In addition, a passage 80' is provided in casting 14, which passage placeschamber 81' in main cylinder 10 in communication with compensatingjchamber 61 At'the bottom of compensating chamber 58 islocated a check valve denotedin itsentir'ety by the numeral 82 Checkvalve 82 comprises a casting 83' in the form of an inverted cup, having an opening 86 at its top, which is closed from below by valve plate 85. Spring 84 holds plate 85 up against the casting 83. Passage 81, in

casting 13,, places the interior of casting 83 in communication with; chamber 88' in main, cylindef/.102. Compensating piston H is movably mounted: in compensating cylinder 6%. Spring 90, of relatively great strength compared tothe resistance of piston valves and 51', Fig. 6, nor-'- nially holdscompensating piston H up against casting" M at thetop of chamber '51. A port 91 inzcompe'nsating cylinder 66 at its bottom provides communication between chambers 68 and 69..

When piston rod I5 is moved up from its midposition, as shown in Fig. 11,,to its uppermost position, as shown in Fig. 12, the volume of fluid displaced in chamber 81 is less than that of the volume created in chamber 88. To make up for this difier'ence, compensating piston]! moves up under the influence of its spring to force fluid into chamber 88 via chamber 8land the ports, not shown, in piston H;

As piston l1 and rod l5 move down from its position of Fig. 12 to. the position shown in Fig. 13, the fluid in chamber 88 passes through theports in piston I'linto chamber 8|. Because of the increased volume occupied by rod I5, there is not room in chamber 8| for all thefluid forced out of chamber 88- into chamber 8!. The excessfiuid accordingly flows through passage 802' into chamber 6''! forcing compensating piston H down.

The'l-i'quid' level in the reservoir chamber 69 fallsas in Fig. 12 when the liquid flows into chamber (was the piston 1| rises. As seen in Fig. 13, the liquid level rises when piston H falls; The air in reservoir chamber 69 above the liquid is compressed and expandedas the level rises and falls. The pressure in" chamber 69 does not vary much from atmospheric pressure because the change in volume is only asmall part of the total volume of the air space.

Under normal conditions of construction there will. besomeleakage' around compensating piston 11'. If the vehicle be inoperative for a long enough period of time,.compensa-ting piston H will be moved up by spring 90 as leakage occurs until said piston reaches casting or cap 14' at the top of chamber 61. When the shock absorber is next; used, the fluid-lost by the leakage will be replacedas follows: the-first upward movement of the'piston rod will cause liquidto enter chamber: 88- through check valve 82. Compensating p'i'ston 'H- is stopped by casting Hr-being prevented thereby from causing high pressure in main cylinder 1-0: The amount of fluid that enters will depend on the amount of upward movement of piston: rod l-5. If a complete upward'strokabeimade by piston I1; compensating piston H will move to the position shown for-it in Fig. 13. upon the next complete downward stroke'of piston Il. If the upward stroke of the piston" rod does: not cause piston IT to reach its extreme upper position, a corresponding less amount of fluid will-'be sucked into cylinder 10. Now when thepi'ston r'o'd moves down, compeneating piston 11* will be at a lesser distance-down than shown for it in Fig. 13: It may, say, be down to the" position shown" for it in Fig. 11.

When the'vehicle on which the shock absorber is mounted is driven fora'long time on a'smo'oth road; the oscillation of the piston rod' I5 Will be limited a" small fraction of'i'ts possible total stroke-. The oscillationof compensating piston l l will be correspondingly small; As leakage takes place past piston TI, said piston will gradu'ally" move toward its-upper stop which is the casting 14, because no'liquid can enter chamber 61 to replace the loss until piston H arrives at said stop. Then when there is a relatively large downward stroke of piston rod I5, fluid will be forced into chamber 61, Fig. 13.

The compensating spring 90 is strong enough so that with ordinary motions, the pressure resulting from the upward motion of piston ll opposes but does not overcome the upward pressure in chamber 61 caused by piston H. If the upward velocity of piston rod l were high enough relatively to the strength of spring 99 or of said spring were too weak, the upward motion of the piston H would'cause piston H to be forced down against spring 90, fluid being sucked in at the same time through check valve 82 to compensate both for the volume evacuated by piston rod [5 in leaving chamber 8| and the increased volume of chamber '61. Openings 92 in cylinder i6 will permit the return of. fluid to reservoir chamber 69 when iston H is forced far enough down to clear them. Once the fluid escapes through openings 92, there is no further downward motion of piston II. This also serves to prevent the jamming of spring 90 so that all its coils are closed. When this occurs, if holes 92 were omitted, any further introduction of fluid into chamber 91 upon sudden downward motion of piston I! would subject the shock absorber to excessive stress. 1

The strength of the compensating spring'llli, influences the retarding force of main piston H. The force pushing compensating piston ll upward will be less at the top of its'stroke than at the bottom,'because with said piston at the top, compression spring 90 is extended, and with said spring at the bottom the spring is compressed. The maximum damping action on main piston I1 is, therefore, less when the compensating pistonis near. the top of its stroke. The time when maximum damping is needed is on the rebound. The upward motion of' pistonv I! on which-a high degree of damping is required will always be preceded by a large downward displacement of said piston. This downward displacement of piston I1, because of the entrance of piston rod [5 into chamber 81 at the same time moves compensating piston H down, resulting in the compression of spring 90. Thus on the rebound, that isv when piston '11 jumps up, spring 90 exerts its maximum'upward pressure resulting in the exertion of the maximum" damping force on said piston.

To a great extent, the features discussed above for the construction of Figs. 11-14 also apply to the construction in which the compensating piston is in alignment with the mainpiston, Figs. 1-10. With the latter construction, the stroke of the compensating piston allows for part only of the fluid displaced by the piston rod, an overflow being provided to take care of the full stroke of the piston rod 15. In Figs. 11-14,

the compensating piston provides for the full stroke of the piston rod l5, the overflow 92 being provided for other reasons as noted above.

The relatively strong pressure of theirsprings against compensating pistons-35 and H as noted before, produces a high pressure in chambers 38 and 54, Fig. 2, and in chambers 8| and 88, Fig. 12.

This will tend to push piston rod out when it is in any position other than its extreme upper position. That this is so is because the area exposed to downward fluid pressure is less on the top of piston l1, than the area exposed to upward pressure against the bottom of said piston. The presence of piston rod l5 at the upper surface of piston l1 prevents an area equal to the cross section-of the piston from being exposed to the fluid. ,Because the area of piston rod [5 is small to that of piston l1, this unbalanced force is not objectionable. The larger diameter of piston I1 and hence that of the main cylinders l8 and Ill is made, the less will be the efiect of said unbalanced force. By using a larger diameter .for piston l1 and the main cylinders, the volume of liquid required to pass the piston will be increased requiring larger fluid passages. Larger passages are easier to manufacture and less critical to tolerance.

Ports in compensating cylinder 29 and ports 92 in compensating cylinder 66, besides limiting the travel of compensating pistons 35 and II, respectively, serve as overflows from the compensating cylinders to. the reservoirs.- If such overflows were not provided, jolts which would be severe enough to draw fluid from the reservoirs through check valves 21 and -82 would soon have fluid in the main and compensating cylinders with no place to go when the piston rod was moved down into the main cylinders. For a jolt to be severe enough to draw in fluid into the main cylinders through'said check valves, said jolt must develop suflicient resistance'to passage of fluid through the main pistons to overcome the pressure of springs 51 and against compensating pistons 35 and H.

The term cylinder as used in the claims is not necessarily limited to a cylindrical body, but is intended to be broad enough to cover other forms having corresponding istons.

We claim:

Y 1. In a shock. absorber of the fluid-flow type the combination of a plurality of tubular members arranged to provide a main cylinder portion, a compensating cylinder portion and a reservoir around said cylinder portions, a main piston and piston rod therefor reciprocably mounted in the main cylinder portion, said rod extending through one end of the main cylinder portion, a passageway connecting the main cylinderportion and the compensating cylinder portion-substantially at said end, a compensating piston reciprocably mounted in thecompen'sating cylinder portion, a spring pressing the compensating piston toward said end, a passage connecting the opposite end of the mainlcylinder portion with the reservoir, a check valve permitting flow through the said latter passage to the main cyl,- inder portion but not from said main cylinder portion, and overflowmeans, in communication with the main' cylinder and the reservoir,-,-.permitting escape of fluid. to the reservoir when a predetermined fluid pressure is exceeded in the main cylinder. 3

' 2. Ina shock absorber of the fluid-flow type, the combination of a main cylinder and a compensating cylinder communicating with the main cylinder for interflow of fluid, a main piston and a piston rod therefor reciprocably mounted in the main cylinder, said rod extending through one end of the main cylinder, means in the main piston permitting flow through the main piston inboth directions, said means including valve elements permitting said flow in both directions but each element in itself permitting flow through the main'piston in one direction only, a compensating piston reciprocably mounted in the compensating cylinder, and a spring pressing the compensating piston to exert pressure in the main cylinder in a direction to opposethe outward motion of themain pistonandpiston rod,

the pressure 'exertedbythe compensating piston being normally in substantial excess of the .resistthe main cylinder portion-and the compensating cylinder portionsubstantially at said end,:means in the main piston permitting flow through the main pistonin both directions,:said means including valve elements permitting said now "in both directions buteach element'in itself permitting flow through the mainpiston in one direction only, a compensating piston reciprocably mounted in the compensating cylinder portion, F2. spring pressing the compensating piston'toward said end,a passage connecting'the opposite end of the main cylinder portion with the reservoir, a check valve permitting the flow oi fiuid'througli said latter passage to the main cylinder'portion but not from saidmain'cylinder portion, :and overflow means in communication with the main cylinder and the'reservoir, permitting escape "of fluid to the reservoir whena predeterminedfluid pressure is exceeded'in the main cylinder.

4. In a shock absorber of'the fluid-flowtype, the combination of a-main cylinder, a vmainpiston and a piston rod therefor "reciprocably mounted in the main cylinder, said rod extending through one end of the main cylinder, means in the main piston, including valve elements, permitting flow through the .main piston .in both directions, at least one valve element permitting flow through the main piston .in each direction, the relative resistance to theflow of fluid through the elements being such that said resistance is greater for fluid passing through the piston in a direction away from said end, :a compensating: cylinder, a passageway connecting the'cylindera substantially at said end,fla compensating piston reciprocably mounted in the compensating cylinder, and a spring pressing the compensating piston toward said passage. r

5; In a shock absorber of .the fluid-flow type, the combination of 'a main cylinder, a main piston and a piston rod "therefor .reciproca'bly mounted in the main cylinderjsaid rod extending through one end of the main cylinder, means in the main piston, including valve elements, permitting flow through the main piston in bothdirections, but each valve element .initself permitting flow in'one direction only, at least one velement permitting flow through the main piston in each direction, a compensating cylinder, a passageway connecting the cylinders substantially at said end, a compensating piston reciprocahly mounted in the compensating cylinder, and-a spring pressing the compensating piston to exert pressure inthe main cylinder in a direction to oppose the outward motion of the main piston and piston rod, the pressure exerted by the compensating piston being normally in substantial excessto the resistance offered, by the flow of fluid through the main piston when the latteris moved in an outwarddireotion in the main cylinder. i g

6-. In a shock absorber of thefiuid-flow type,

the combination :of a main cylinder and a compensating cylinder communicating with the main cylinder'for interflow of fluid, a main'piston and a piston rod therefor reciprocably mounted in the main cylinder, said rod extending through one end of the main cylinder, means in the .main piston, including valve elements, permitting flow through the main piston in both directions, but each valve element in itself permittingflowthroughthe main piston in one direction only, there being a pluralityof valve-elements permitting flow through the .pistonlaway from said end, said latter elements opening 'up to a greater extent successively for the flow of fluid through them in accordance with'the increaselin pressure developed by the pistoniduring the. motion of said piston toward saidend, a compensating. piston ,.recipr.ocably..mounted in the compensating vcylinclelgzand a spring urging the compensating piston to exert pressure .in the main cylinder in a direction to oppose theoutward motion of the mainpiston-and the :piston rod, the pressure exerted Joy the compensating piston beingnormallyin excess or theresi'stance offered by the flow of fluid'through the main piston as the latter valve elements open upsuccessively as the main piston'is moved outward direction in themain cylinder.

'7. In a shock absorber for use on a springmounted vehicle, a cylinder, a piston and'piston rod reciprocably mounted in the cylinder, the cylinder and'pistonirod' being :sorconnectedto the vehicle that, upon compression of the vehicle springs, the piston rod and piston travel in one direction in the cylinder, 'and in the opposite direction therein uponrecoil oisaid springs, and a pluralityof valve elements-on the piston :permitting flow through :the piston in both "direc tions, but each element .in itself permitting flow through the piston in one direction only, there being a plurality of valve elements permitting flow through the piston'away from'the .endpf the cylinder-toward which the piston moveslupon its 21360011, said latter elementszopening up to a greater extent with resilient resistanceysuccessively for the flow of fluid through them in accordance with the increase in speed of the piston toward said latter end upon recoil.

-8. In a shock absorber of the fluid-flow type the combinationoi a main cylinder, acompensatin'g cylinder, a reservoir,- a main'pi-stonf.andpiston rod therefor'reciprocably mounted :in the main cylinder, said rod extending through oneend of the main oylinderga passagewaynonneicting the main cylinder andlthe compensating cylinder substantiallyat said end, a compensating piston .reciprocablyLmOunted in the compensating cylinder, .a springurgingthe compensating piston'toward said end, a passageway connecting the main cylinder with the reservoir substantially at the opposite end of 'th emain cylinder, a check valve permitting flow through the latter passage way to the main cylinder but not from the main cylinder, check valve means permitting flow through the main piston in one direction, other check valve means permitting fiow through main piston in the opposite direction, and overflow means in communication with the main cylinder and the reservoir, permitting escapeof fluid to the reservoir when a predetermined fluid pressure is exceeded 'in'the main cylinder.

9. In a shock absorber of the finid-flow' type the cornbinationof a main cylindena compensating cylinder in substantial axial alignment with the main oylindena main piston'and 'pisten rod '13 therefor reciprocably mounted in the main cylinder, saidrod extending through one end of the main cylinder and passing through and out of the compensating cylinder, a passageway at said end connecting the main and compensating cylinders, a compensating piston in the compensating cylinder slidably mounted on. said rod, a spring urging the compensating piston toward said end, a reservoir; a passageway connecting the main cylinder with the reservoir substantially at the opposite end of the main cylinder, a check valve permitting flow through the latter passageway to themain cylinder but not from the main cylinder, the main piston being constructed to permit flow at a restricted rate by it in both directions, and overflow means in communication with the main cylinder and the reservoir, permitting escape of fluid to the reservoir when a predetermined fluid pressure is exceeded in the main cylinder.

10. In a shock absorber of the fluid-flow type the combination of a main cylinder, a compensating cylinder located to the side of the main cylinder, a main piston and piston rod therefor reciprocably mounted in the main cylinder, said rod extending through one end of the main cylinder, the compensating cylinder communicating with the main cylinder substantially at said end, a compensating piston in the compensating cylinder, a spring urging the compensating, piston toward said end to exert pressure in the main cylinder in a direction to oppose the motion of the main piston toward said end, a reservoir, a passageway between the opposite end of the main cylinder and the reservoir, a check valve permitting flow through the passageway to the main cylinder but not from the main cylinder, the main piston being constructedto permit flow at a restricted rate by it in both directions, and overflow means in communication with the main cylinder and the reservoir,. permitting escape of fluid to the reservoir when a predetermined fluid pressure is exceeded in the main cylinder.

11. In a shock absorber of the fluid-flow type the combination of a main cylinder, a compensating cylinder in substantial axial alignment with the main cylinder, a main piston and piston rod therefor reciprocably mounted in the main cylinder, said rod extending through one end of the main cylinder and passing through and out of the compensating cylinder, a passageway substantially at said end connecting the main and compensating cylinders, a compensating piston in the compensating cylinder slidably mounted on said rod, a spring urging the compensating piston toward said end, a reservoir, a passageway conmeeting the main cylinder with the reservoir substantially at the opposite end of themain cylinder, and a check valve permitting flow through the latter passageway to the main cylinderbut not from the main cylinder, the main piston being constructed to permit flowat a restricted rate by it in both directions, said compensating cylinder being provided with a port located at a substantial axial-distance from the end of the main cylinder through which the piston rod passes, said port connecting the compensating cylinder with the reservoir, flow from the main cylinder via the compensating cylinder through said port to the reservoir being blocked by the compensating piston when the compensating piston is less than the axial distance of said port from that end of the main piston through which the piston rod passes, the entrance of the rod into the main cylinder forcing the compensating piston away from said latter end until the compensating piston is moved sufficiently to clear the port for flow through said port from the compensating cylinder to the reservoir.

12. In a shock absorber of the fluid-flow type the combination of a main cylinder, a compensating cylinder located to the side of the main cylinder, a main piston and piston rod therefor reciprocably mounted in th main cylinder, said rod extending through one end of the main cylinder, the compensating cylinder communicating with the main cylinder substantially at said end, a compensating piston in the compensating cylinder, a spring urging the compensating piston toward said end to exert pressure in the main cylinder in a direction to oppose the motion of the main piston toward said end, a reservoir, a passageway between the opposite end of the main cylinder and the reservoir, a' check valve permitting flow through the passageway to the main cylinder but not from the main cylinder, the main piston being constructed to permit flow at a restricted rate by it in' both directions, said compensating cylinder being provided with a port located a substantial axial distance from the end of the main cylinder through which the piston passes, said port connecting the compensating cylinder with the reservoir, flow from the main cylinder via the compensating cylinder through said port to'the reservoir being blocked by the compensating piston when the compensating piston is less than said axial distance of said port, the entrance of the rod into the main cylinder forcing the compensating piston away from said latter end until the compensating piston is moved sufficiently to clear the port for flow through said port from the compensating cylinder to the reservoir.

13. In a shock absorber of the fluid-flow type the combination of a main cylinder, a compensating cylinder in substantial axial alignment with the main cylinder, a casing surrounding said cylinders providing a reservoir'between said cylinders and the casing, a main piston-and piston rod therefor reciprocably mounted in the main cylinder, said rod extending through one end of the main cylinder and passing through and-out of the compensating cylinder, a passageway' at said end connecting the main and compensating cylinders, a compensating piston in the compenksating cylinder slida bly mounted on'said rod, a spring urging the compensating piston toward said end, a passageway connecting the main cylinder with the reservoir substantially at the opposite end of the main cylinder from said one end, a check'valve permitting flow through the latter passageway to the main cylinder but not from the main cylinder, the main pistonbeing constructed to permit flow at a restricted rate by it in both directions, and overflow means in communication with the main cylinder and the reservoir, permitting escape of fluidto the reservoir when a predetermined pressure is exceeded in the'main cylinder.

14. In a shock absorber of the fluid-flow "type the combination of a main cylinder, a compensating cylinder located to the side of the main cylinder, a casing surrounding said cylinders providing a reservoir between said cylinders and the casing, a main piston and piston rod therefor reciprocably mounted in the main cylinder, said rod extending through one end of the main cylinder, the compensating cylinder communicating through an opening with the main cylinder sub- 'stantially at said end, a compensatingpiston in .inder, the main piston being constructed to permit flow at a restricted rate by it in "both directions, and overflow means in communication with the .main cylinder and the reservoir permitting escape of fluid to the reservoir when a predetermined fluid pressiue is exceeded inthe main cylinder.

15. A shock absorber as claimed in claim 9 in which the compensating cylinderis provided with a port located on the side of the compensating piston away from the main cylinder, said port connecting the compensating cylinder with the reservoir, flow from the maincylinder via the compensating cylinder through said port to the reservoir being blocked by compensating piston except for leakage past the compensating piston.

16. In a shock absorber of the fluid-flow type the combination of a main cylinder, a compensating cylinder located to the side of the main cylinder, an, end piece forming a closure forthe main .cylinder extending laterally to form an end closure also for the compensating cylinder, a chamber located axially beyond said end piece, said piece forming one end of the chamber, a second end piece spaced axially from the first end piece forming the other and far end of said chamber, a passageway provided in said first end piece for fluid communication between the main and compensating cylinders, a main piston and piston rod therefor reciprocably mounted in the main cylinder, said rod extending slidably through both of said end pieces, a'spring urging the compensating piston toward the first of the end pieces to exert pressure through said passageway in the maincylinder in a direction to oppose the motion of the main piston toward said end, a reservoir, a passageway between the opposite endof the main cylinder and the reservoir, a check valve permitting flow through the latter passageway to the main cylinder but not from the main cylinder, the main piston being con- .structed to permit fiow at a restricted rate byit in both directions, said first end being provided witha port connecting saidchamber with the reservoirfor the flow to the reservoir of leakage to the chamber from the main cylinder along the piston rod, and overflow means in communication with the main cylinder and the reservoir, permitting escape of fluid to the reservoir-when a predetermined pressure is exceeded in the main cylinder.

7 17. In a shock absorber of the fluid-flow type the combination of a main cylinder, acompensating cylinder in substantial axial alignment with the main cylinder, a main piston and piston rod therefor reciprocably mounted in the main cylinder, said rod extending through one end of the .main cylinder and passing through and out of the compensating cylinder, a passageway at saidv end connecting the main and compensating cylinders, acompensating piston in the compensating cylinder slidably mounted on said rod, and a spring urging the compensating piston toward said end.

18. In a shock absorber of the fluid-flow type, the combination of amain cylinder, a main piston and a piston rod therefor reciprocably mounted in the main cylinder, said rod extending through one end of the. main cylinder, meansin the main piston, including valve elements, permitting flow-throughlthe main piston at one time in one direction and at another timein the opposite direction, depending on the direction of motion of the piston, a compensating clyinder in fluid communication with the main cylinder, a compensating piston reciprocably mounted in the compensating cylinder, and'a spring urging the compensating piston to exert fluid pressure in the main cylinder in a direction to oppose the outward motion of the piston rod and main piston, said means in the main piston for permitting flow being constructed to resist in a predetermined manner, the flow of fluid through the main piston in a direction away from said end, the pressure exerted by the compensating piston being normally in substantial excess of the resistance ofifered by the flow of fluid through the main piston when the latter is moved in an.out Ward direction inthe main cylinder.

19. In a shock absorber of the fluid-flow type, the combination ofa cylinder, a piston and a pistonrod therefor reciprocably mounted in the cylinder, a plurality of valve openings in the piston at difierent circumferential distances from each other, considering the longitudinal axis of the piston as a center, a tiltably mounted member normally biased for yieldingly closing said openings against flow offluid through the piston in one direction, a spring reacting against said member for producing itsbias, the axis of thrust of said member'being substantially coaxial with the longitudinal axis ofthepiston, said member being tiltably moved against its, bias to expose said openings when. the piston is moved in the opposite direction with sufiicient velocity to cause the flow of fluid through said openings to overcome the pressure of the spring.

CLYDE R; MAYO. MORRIS KATCHER."

REFERENCES orrno 'The following references are of record in th file of this patent: r

UNITED STATES PATENTS 

